1. FIELD OF THE INVENTION
The invention relates to a well perforating gun incorporating a valve. Upon firing of the gun, the valve is operated to open ports in the tubing string to permit immediate flow of production fluid upwardly through the tubing string.
2. HISTORY OF THE PRIOR ART
The procedure for effecting the perforation of a production formation of a subterranean well in a so-called "underbalanced" condition is an expedient well-known in the art. Briefly, the procedure contemplates the suspension of a packer and a perforating gun on a tubing string. The packer is set above the production formation so as to position the perforating gun adjacent the formation. Steps are then taken to reduce the fluid pressure in the tubing string to a level substantially below the anticipated fluid pressure to be developed by the production formation after perforation; for example, the tubing string may be filled with a light-density fluid, or a swabbing operation conducted therein. The perforating gun is discharged and then one or more ports or fluid passages in the wall of the tubing string adjacent the production formation are opened so as to permit an immediate flow of production fluid from the perforated formation into the tubing string and up to the surface of the well. Due to the pressure differential, or the "underbalanced" condition of the well at the time of perforating, the flow from the production formation is generally quite rapid and results in a flushing of the debris normally resulting from a perforating operation from the perforations in the production formation. The removal of such debris greatly enhances the productivity of the well.
A number of valving devices have heretofore been proposed for opening ports in the tubing string immediately adjacent the production formation subsequent to the firing of the perforating gun. For example, U.S. Pat. No. 4,299,287 to VANN proposes to use a freely falling detonating bar to shift a sleeve valve mounted in series relationship between the tubing string and the perforating gun. Other valving mechanisms are disclosed in the co-pending application Ser. No. 6-551,764, filed Nov. 14, 1983, and assigned to the Assignee of the invention. All of these prior art underbalancing valves were characterized by the incorporation of relatively complex mechanisms with the attendant risk that such mechanisms would fail to operate and thus defeat the entire purpose of perforating the well in an underbalanced condition.